CA2216207A1 - Two-stage laminator apparatus - Google Patents

Abstract

A laminator apparatus (10) includes upper and lower belt assemblies (20, 22) which are supported in closely spaced adjacent relation.
The lower belt assembly (22) includes a stainless steel belt (30) received around first and second metallic rollers (32, 34), and the upper belt assembly (20) includes a teflon impregnated, fiberglass belt (36) received around third and fourth metallic rollers (38, 40), The belt assemblies (20, 22) are positioned such that the first and third rollers (32, 38) form an input nip, and the second and fourth rollers (34, 40) form an output nip, with the endless belts (30, 36) positioned in facing relation. The first roller (32) is heated by an internal cartridge heater (66) to about 200 °C, and a heating platen (68), positioned in abutting relation with an upper portion of the metallic belt adjacent to the first roller, is heated to about 160 °C. Fan-cooled heat sinks (72, 74) are positioned in abutting relation adjacent to the output nip for cooling the metallic fiberglass belt passing therebetween. The belts are rotated for transporting thermoplastic sheet (14, 16) materials between the endless belts from the input nip to the output nip, wherein the lower thermoplastic sheet (16) is initially laminated to the upper thermoplastic sheet (14) under the heat and pressure of the input nip rollers (32, 38), and then fully laminated by passage over the heating platen (68). The laminated plastic sheets are thereafter cooled by passage between the fan-cooled heat sinks (72, 74).

Description

W 096137,255 PCTrUS~6101952 1 TWO-STAGE I~MINATOR APPP~TUS

2 Bac~y~oul~d and Sl~rmnary of the Invention:
, 3 The instant invention relates to laminator apparatus 4 for laminating thermoplastic sheets together, and more particularly to laminator apparatus including ~ace-to-6 face, endless belts ~or transporting thermoplastic sheets 7 through successive pre-laminating, laminating and cooling 8 stations.
9 Belt-type laminator apparatus o~ the general type contemplated herein, have heretofore been known in the 11 art. In general, the prior art laminators typically 12 include only a single heating station for applying heat 13 to the surfaces of the thermoplastic sheets while 14 maintaining the sheets in face-to-face relation. While these single-stage laminators have been e~fective ~or 16 many types o~ thermoplastic sheet materials, there are 17 certain types of thermoplastic sheet materials, such as 18 those materials used in making identification or security 19 cards, which have specific heating and cooling characteristics which are not met by the prior art 21 devices.
22 The instant invention provides a two-stage laminator ~ 23 apparatus comprising upper and lower belt assemblies 24 which are supported in closely spaced adjacent relation.
The lower belt assembly comprises a stainless steel belt 26 received around first and second rollers, and the upper SUBSTITUTE SH EET (RULE 26) W 096/32255 PCTrUS96/04952 1 belt assembly comprises a teflon impregnated, fiberglass 2 belt received around third and fourth rollers. The belt 3 assemblies are supported in a frame structure such that 4 the first and third rollers form an input nip, and the second and fourth rollers form an output nip, with the 6 endless belts in facing relation. The first and second 7 rollers are fixed in position, with the third and fourth 8 rollers being slidably suspended relative to the first 9 and second rollers. The third and fourth rollers are biased downwardly from their suspended position toward 11 the first and second rollers to form spaced, but 12 pressurized input and output nips. The first, or lower, 13 input roller is heated by an internal cartridge heater 14 to a t~ -~ature of about 200~C. The heated input nip thus defines an initial laminating stage. A heating 16 platen, positioned in abutting relation with an upper 17 portion of the metallic belt adjacent to the first roller 18 is heated to a temperature of about 160~C to define a 19 full laminating stage. Fan cooled heat sinks are positioned in abutting relation adjacent to the output 21 nip for cooling the metallic and fiberglass belts passing 22 therebetween.
23 In particular, the instant apparatus is useful for 24 laminating a security card system comprising an amorphous copolyester backing sheet, a polyvinyl chloride (PVC) 26 cover sheet, and a security image positioned between the W ~96132255 PCTAUS96/04952 1 sheets. The security image is preferably reverse printed 2 via conventional thermal dye transfer technology onto the 3 underside of the cover sheet so that the security image 4 is securely located between the sheets where it cannot be tampered with. When viewed through the upper surface of 6 the cover sheet, the reverse printed image appears in its 7 correct orientation. The amorphous copolyester and PVC
8 sheets are compatible polymers which effectively fuse 9 together under heat and pressure without the use of an intermediate adhesive. In use, the rotating belts are 11 operative for transporting the overlapping cover and 12 backing sheets between the input nip and the output nip.
13 The overlying sheets are inserted into the input nip of 14 the apparatus with the cover sheet facing downwardly, wherein the cover sheet is initially laminated to the 16 upper backing sheet under the heat and pressure of the 17 input nip rollers. After the initial lamination, passage 18 over the adjacent heated platen further heats the pre-19 laminated sheets while in a fixed position, wherein the sheets are able to fully fuse or laminate together. The 21 fused, laminated sheets are thereafter cooled by passage 22 between the fan-cooled heat sinks.
23 Accordingly, among the objects of the instant 24 invention are the provision of a two-stage laminating device wherein two thermoplastic sheets are pre-laminated 26 under heat and pressure, fully laminated under heat 1 alone, and then cooled; the provision of a laminating 2 device including facing endless belts for transporting 3 sheet materials through a pre-lamination station, a full 4 laminating station, and a cooling station; and the provision of a laminating device including a heated input 6 nip, a heated platen and fan cooled heat sinks.
7 Other objects, features and advantages of the 8 invention shall become apparat as the description thereof 9 proceeds when considered in connection with the accompanying illustrative drawings.

12 Description of the Drawings:
13 In the drawings which illustrate the best mode 14 presently contemplated for carrying out the present invention:
16 Fig. 1 is a front view of the laminator apparatus of 17 the instant invention;
18 Fig. 2 is a rear view thereof;
19 Fig. 3 is a top view thereof; and Fig. 4 is a cross-sectional view thereof taken along 21 line 4-4 of Fig. 3.

23 D~scription of the Preferred ~mbodiment:
24 Referring now to the drawings, the laminator apparatus of the instant invention is illustrated and 26 generally indicated at 10 in Figs. 1-4. As will W O 96132255 PCT~US96/04952 1 hereinafter be more fully described, the instant 2 laminator apparatus 10 is operative for laminating face-3 to-face thermoplastic sheet materials, such as those 4 types of sheet materials used in constructing security cards. More specifically, the instant invention 10 has 6 been found to be particularly useful in fusing a security 7 card system developed by Minnesota Mining and 8 Manufacturing Company of Saint Paul Minnesota, and 9 described in U.S. Patent Application No. 08/128,484 which lo is incorporated herein by reference.
11 The subject security card system generally indicated 12 at 12 in Fig. 4, comprises a backing sheet 14, a cover 13 sheet 16, and a security image (not shown), with the 14 security image preferably being reverse printed on the inner surface 18 of the cover sheet 16 so that it is 16 located between the laminated sheets 14, 16 when secured 17 together. When viewed through the upper side of the 18 cover sheet, the reverse printed security image appears 19 in its correct orientation. The backing and cover sheets 14, 16 are laminated in direct contact together without 21 an intermediate layer of adhesive, wherein the backing 22 sheet 14 preferably comprises an amorphous copolyester 23 film, and the cover sheet 16 comprises a rigid polyvinyl 24 chloride film. The amorphous copolyester backing sheet 14 is preferably pigmented with titanium dioxide so that 26 it is opaque white, while the PVC cover sheet 16 is W O 96/32255 PCTrUS96/04952 1 preferably transparent, although other color schemes and 2 arrangements are also suitable. In most instances, the 3 backing sheet 14 is considerably thicker than the cover 4 sheet as it is intended to provide most of the rigidity and strength of the assembled card 12. For example, the 6 backing sheet 14 preferably has a thickness of between 7 about 20 and 22 mils, and the cover sheet 16 preferably 8 has a thickness of between about 7 and 10 mils for a 9 total card thickness of between about 27 and 32 mils.
The particular advantage of the subject security card 11 system 12 is that good adhesion can be achieved between 12 PVC and amorphous copolyesters at relatively low 13 temperatures, e.g., at temperatures of about 150~C. The 14 adhesion can be effectively achieved because both amorphous copolyesters and PVC are softened during the 16 lamination process, and both contract on cooling at about 17 the same rate, thereby reducing warping problems 18 encountered with other existing card materials.
19 The instant laminator apparatus 10 comprises upper and lower belt assemblies generally indicated at 20 and 21 22, which are supported in closely spaced adjacent 22 relation by a frame assembly comprising a bottom wall 24, 23 and parallel front and rear walls, 26 and 28 24 respectively.
The lower belt assembly 22 comprises a stainless 26 steel belt generally indicated at 30 received around W 096132255 PCTrUS96/04952 1 first and second metallic rollers 32, 34 respectively, 2 and the upper belt assembly 20 comprises a teflon 3 impregnated, fiberglass belt generally indicated at 36 4 received around third and fourth metallic rollers, 38 and 40 respectively. Both the stainless steel belt 30 and 6 the fiberglass belt 36 preferably have thicknesses of 7 about .003 inches. The steel belt 30 is commercially 8 available from Belt Technologies of Agawam, MA, and the 9 fiberglass belt 36 is available from Greenbelt Industries, Inc. of Buffalo, NY. The rollers 32, 34, 38, 11 40 preferably comprise aluminum rollers having shafts 12 32S, 34S, 38S, 40S. It is pointed out that shafts 32S
13 and 38S are hollow, while shafts 34S and 40S are solid.
14 The belt assemblies 20, 22 are supported in the frame such that the first and third rollers 32, 38 from 16 an input nip, and the second and fourth rollers 34, 40 17 form an output nip, with the endless belts 30, 36 in 18 facing relation. The first and second rollers 32, 34 are 19 fixed in position, with the third and fourth rollers 38, 40 being slidably movable relative to the first and 21 second rollers 32, 34. More specifically, the shaft of 22 each roller is received through a pair of spaced bearing 23 mounts generally indicated at 42A, 42B, 42C, and 42D.
24 Each bearing mount 42 comprises a bearing 44A, 44B, 44C, 44D which is supported in a bearing holder 46. Bearings 26 44A and 44C each comprise a roller-type bearing, while W O 96/32255 PCTrUS96/04952 1 bearings 44B and 44D comprise sleeve-type bearings.
2 Furthermore, the sleeve bearings 44B and 44D are mounted 3 in a hardened outer sleeve 45. Each bearing holder 46 4 includes a recess 48 for receiving the bearing 44 therein, and further includes grooves 50 in the side 6 edges thereof. The grooves 50 of the bearing mounts 42 7 are slidably received in respective slots 52 in the front 8 and rear walls 26, 28 of the frame assembly so that the 9 bearing holder 46 engages both the inner and outer surfaces of the walls 26, 28. The bearing mounts 42A and ll 42B rest against the bottom of their respective slots 52, 12 and thus maintain the first and second rollers 32, 34 in 13 a fixed vertical position. It is pointed out that the 14 recesses 48B in the bearing mounts 42B (second roller 34) are elongated in a horizontal direction to allow sliding 16 horizontal movement of the axis of the second roller 34 17 with respect to the first roller 32. In this connection, 18 a set 54 is extended through a threaded opening in the 19 side wall of the bearing mount 46B and engaged with the hardened outer sleeve 45 to adjust the distance between 21 the axis of the first roller 32 and the axis of the 22 second roller 34. This set screw arrangement is 23 operative for adjusting the parallelism of the first and 24 second roller axes as well as for taking up or tightening slack in the steel belt 30. The bearing mounts 42D for 26 the fourth roller 40 have the same elongated recess 48D

W 09613'~255 PCTAUS96/04952 1 and set screw 54 for adjus~ment of the fourth roller axis 2 with respect to the third roller axis.
3 The bearing mounts 42C, 42D for the third and fourth 4 rollers 38, 40 are suspended in the frame assembly by screws 56 which extend downwardly through spaced 6 suspension bars 58 attached to the front and rear walls 7 26, 28. The head 60 of the screw 56 rests on top of the 8 bar while the shaft 62 passes through an opening (not g shown) in the bar 58 and extends into a threaded bore (no shown) in the top of the respective bearing holder 46.
11 A compression spring 64 is received around each screw 56 12 and captured between the top of the respective bearing 13 holder 46 and the bottom of the respective suspension bar 14 58 to bias the third and fourth rollers 38, 40 downwardly from their suspended position toward the first and second 16 rollers 32, 34. Rotation of the screw 56 permits 17 adjustment of the vertical spacing between the third and 18 first rollers 38, 32 (input nip rollers) and the fourth 19 and second rollers 40, 34 (o~L~uL nip rollers). In this regard, the belt assemblies 20, 22 are adjusted so that 21 there is at 25 mil spacing between the input rollers 32, 22 38 and between the ouL~uL rollers 34, 40, the spacing 23 being slightly smaller than the combined thickness of the 24 security card sheets (27-33 mils). Since the third and fourth rollers 38, 40 are biased downwardly toward the W 096/3t2S5 PCTrUS96/n4952 1 first and second roller 32, 34, the roller pairs form 2 spaced, but pressurized input and output nips.
3 The first, or lower, input roller 32 is heated by a 4 conventional cartridge heater 66 to a temperature of between about 190~C and about 215~C, but more preferably 6 to a temperature of about 200~C. The cartridge heater 66 7 is slidably received in the center of the hollow roller 8 shaft 32S and is energized by a conventional electric g source (not shown). The input nip (rollers 32, 38) thus defines an initial or pre-laminating stage for fusing the 11 cover and backing sheets 14, 16 together under pressure 12 and heat.
13 Referring now to Fig. 4, a full laminating stage is 14 defined by a 1/2 inch thick aluminum heating platen 68, positioned in abutting relation with an upper portion of 16 the steel belt 30 adjacent to the first roller 32. The 17 platen 68 is preferably heated to a temperature between 18 about 150~C and about 170~C, and more preferably to a 19 temperature of about 160~C. Heating of the platen 68 is accomplished by means of a rubber plate heater 70 glued 21 to the bottom surface of the platen 68. A rubber plate 22 heater 70 of the type contemplated is available from 23 Hotset, Inc. of Battle Creek, MI. Alternatively, other 24 heating devices, such as cartridge-type heaters, could be used to heat the platen 68.

W 096J3~255 PCTrUS96/04952 1 In order to cool the belts 30, 36 and the laminated 2 sheets 14, 16 held therebetween, first and second fan 3 cooled heat sinks generally indicated at 72, 74 4 respectfully, are positioned in abutting relation adjacent to the output nip (rollers 34, 40). More 6 specifically, a first aluminum heat sink 72 is positioned 7 between the front and rear walls 26, 28 of the frame, 8 with the body portion 72B in abutting relation with the 9 upper portion of the steel belt 30. Fasteners 76 extend through the front and rear walls 26, 28 of the frame and 11 into openings (not shown) in the heat sink 72 to fixedly 12 secure the heat sink 72 in position. A second heat sink 13 74 is positioned between the front and rear walls 26, 28 14 of the frame assembly with the body portion thereof 74B
in abutting relation with the lower portion of the 16 fiberglass belt 36. A second set of fasteners 78 extend 17 through vertical slots 80 in the frame walls 26, 28 and 18 into the second heat sink 74. Springs 82 are secured 19 between the fastener pairs to draw the second movable heat sink 74 downwardly into compressing relationship 21 with the first fixed heat sink 72. The fins 72F, 74F of 22 the heat sinks 72, 74 extend perpendicular to the 23 direction of travel of the belts 30, 36 wherein first and 24 ~co~ fans 82, 84 mounted to the rear wall of the frame respectively blow air over the fin surfaces 72F, 74F in 26 a direction perpendicular to the direction of belt W O 96/32255 PCTrUS96/04952 1 travel. To facilitate rapid air movement and optimize 2 cooling, the air is moved through openings 86, 88 in the 3 front and rear walls 26, 28 of the frame assembly.
4 In use, the belts 30, 36 are rotated simultaneously in opposite directions for transporting the overlapping 6 cover and backing sheets 14, 16 between the endless belts 7 from the input nip to the output nip. Rotation of the 8 belts 30, 36 is accomplished via an electric motor 9 generally indicated at 90 and gear system. The body 92 of the electric motor 90 is mounted to a bracket 94 11 attached to the rear wall 28 of the frame assembly. The 12 drive shaft 96 of the motor 90 includes a worm gear 13 portion 98 for rotating a drive gear 100 mounted on the 14 rear end of the shaft 34S of the second roller 34 (Fig.
2, 3). Rotation of the lower belt assembly 22 is 16 transferred to the upper belt assembly 20 by a pair of 17 interme~h;ng transfer gears 102, 104 mounted on the front 18 ends of the shaft 34S, 40S of the second and fourth 19 rollers 34, 40 (Fig. 1). The motor 90 and gear assembly are preferably timed for transporting cards through the 21 apparatus at a rate of about 0.25 inches per second. The 22 instant device is thus operative for transporting a 23 conventional size ID card through the laminator at a rate 24 of about 1 card per minute.
The apparatus 10 further includes upper and lower 26 steering as~emblie~ generally indicated at 106 and 108 W 096132255 PCTfUS96/049~2 1 for main~;n;ng proper alignment and rotation of the 2 belts 30, 36 on their respective rollers. Each steering 3 assembly 106, 108 comprises a shaft llO mounted between 4 the front and rear walls 26, 28 of the frame. The shaft lloU of the upper steering assembly 108 extends 6 immediately beneath the upper portion of the fiberglass 7 belt 36 adjacent the input nip, and the shaft llOL of the 8 lower steering assembly extends immediately above the 9 lower portion of the steel belt 30 adjacent to the input nip (Fig. 4). Mounted on each of the shafts 110 is a 11 mating pair of truncated cone rollers 112 with the larger 12 diameter ends of the roller 112 facing toward the outer 13 ends of the shafts 110. In this regard, as the belts 30, 14 36 rotate, if either belt should skew toward one side or the other, the belt will ride upwardly on the 16 corresponding truncated roller 112, wherein it will be 17 urged back downwardly into its normal rotating position.
18 The apparatus 10 is intended to be used with the 19 cover sheet 16 of the card system facing downwardly and the backing sheet facing 14 upwardly. As the overlying 21 sheets 14, 16 are fed into the input nip, the backing and 22 cover sheets 14, 16 are pressed together under the 23 pressure of the nip while the cover and backing sheets 24 14, 16 are heated by the heated lower roller 32 of the input nip. The pressure of the input nip squeezes out 26 air bubbles from between the sheets 14, 16 prior to W 096132255 PCT~US96/049~2 1 laminating, and further maintains the cover and backing 2 sheets 14, 16 in proper registration during initial 3 heating by the roller 32. MaintA;n;ng the sheets 14, 16 4 in proper registration during the initial heating is extremely important, since the plastic materials become 6 somewhat soft, and movement of the sheets at their 7 interface while in a molten state will cause smudging or 8 smearing of the security image printed on the inner side 9 18 of the cover sheet 16. After the initial lamination, the pre-laminated sheets 14, 16 are transported over the 11 heated platen 68 which further heats the sheets for a 12 longer duration while in a fixed position wherein they 13 are able to fully fuse or laminate together. It is noted 14 that the longer exposure to heat over the platen 68 significantly softens the upper backing sheet 14 to a 16 point wherein the surface grain or texture of the 17 fiberglass belt 36 can be unwantedly imprinted on the 18 back surface 114 of the backing sheet 14. In this 19 connection, a lower portion of the fiberglass belt 36 directly above the heating platen 68 is cooled by a fan 21 116~ The air directed across the fikerglass belt 36 22 keeps the back surface 114 of the backing card 14 23 sufficiently cool and rigid so as not to be imprinted 24 with the surface texture of the fiberglass belt 36.
The la~inated sheets 14, 16 are thereafter cooled to 26 almost room temperature by passage between the fan-cooled -W 096132255 PCT~US96/04952 1 heat sinks 72, 74. The sinks 72, 74 effectively remove 2 almost all of the heat from the sheets 14, 16 prior to 3 exiting from the apparatus between the ouL~u~ nip.
4 It can therefore be seen that the instant invention provides an effective laminating apparatus 10 which is 6 effective for pre-laminating a pair of sheet materials 7 under pressure and heat, further heating the pre-8 laminated sheets to achieve a full bond, and then cooling 9 the laminated sheets prior to exiting the apparatus. The apparatus achieves these objectives by providing a 11 pressurized input nip having a heated roller 32. Sheet 12 materials passed through the input nip are laminated 13 under the pressure and heat of the nip. The pre-14 laminated materials are then passed over a heated platen 68 for further heating of the sheets materials to achieve 16 a full bonding of the materials. The fully laminated 17 sheets are then cooled by fan cooled heat sinks 72, 74 18 prior to passage out of the apparatus through a 19 pressurized output nip. For these reasons, the instant invention is believed to represent a significant 21 advancement in the art which has substantial c A~cial 22 merit.
23 While there is shown and described herein certain 24 specific structure embodying the invention, it will be manifest to those skilled in the art that various 26 modifications and rearrangements of the parts may be made CA 022l6207 l997-lO-09 W 096/3225S PCTrUS96/04952 1 without departing from the spirit and scope of the 2 underlying inventive concept and that the same is not 3 limited to the particular forms herein shown and 4 described except insofar as indicated by the scope of the appended claims.

Claims (10)

1. Apparatus (10) for fusing a first polymeric sheet (16) in face-to-face relation with a second polymeric sheet (14) comprising:
a first belt assembly (22) including a first endless belt (30) received around first and second rollers (32, 34);
a third roller (38) mounted in cooperation with said first roller (32) to form an input nip with said first roller (32), said first and third rollers pressing said sheets (14, 16) together in face-to-face relation to define a two-piece structure (12), said first polymeric sheet (16) being received adjacent said first roller (32) and said second polymeric sheet (14) being received adjacent said third roller (38) while said sheets are being pressed together;
means (66) for heating only said first roller (32) such that only said first polymeric sheet (16) is heated, said pressure and said heat achieving an initial fusing of said first and second polymeric sheets; and heated platen means (68) for applying heat to said first polymeric sheet (16), said heated platen means being in thermal communication with an underside of said belt (30), said two piece structure (12) being supported on an upper side of said belt and being transported from said input nip over the surface of said heated platen means wherein further heat is applied under ambient pressure to said first polymeric sheet.

2. The apparatus of claim 1 further comprising cooling means (72, 74) downstream of said heated platen means (68) for cooling said sheets.

3. A method for fusing a first polymeric sheet (16) in face-to-face relation with a second polymeric sheet (14), comprising the steps of:
arranging said first and second polymeric sheets (14, 16) in face-to-face relation to define a two-piece card structure (12);
applying pressure to said face-to-face sheets (14, 16) to press said sheets together;
preheating only the first polymeric sheet (16) while said sheets are being pressed together, said pressure and heat achieving an initial fusing of the sheets;
removing the applied pressure from the initially fused sheets; and then applying heat to only said first polymeric sheet (16) of the initially fused two-piece card structure (12) to achieve full fusion of the first and second polymeric sheets (14, 16) to each other.

4. The method of claim 3 further comprising the step of cooling said fused sheets of said two-piece structure (12).

5. The method of claim 3 wherein said step of applying pressure to said face-to-face sheets (14, 16) comprises to step of pressing said sheets together in face-to-face relation in a nip roller structure (32, 38) to define a two-piece card structure (12) having a first side defined by said first polymeric sheet and an opposing second side defined by said second polymeric sheet.

6. The method of claim 5 wherein said step of preheating comprises the step of heating said first side of said two-piece card structure (12) to a first temperature while said card structure (12) is being pressed together in said nip roller structure (32, 38) such that said heat softens the first polymeric sheet (16) and further such that heat passes through said first polymeric sheet (16) to heat an inner surface of said second polymeric sheet (14), said heat and said nip pressure achieving an initial fusing of said first and second polymeric sheets (14, 16) without any air bubbles being formed therebetween.

7. The method of claim 5 wherein said step of applying heat to only the first polymeric sheet (16) comprises the step of heating said first side of said two-piece structure (12) to a second temperature without deforming said second polymeric sheet (14).

8. The method of claim 6 wherein said step of applying heat to only the first polymeric sheet (16) comprises the step of heating said first side of said two-piece structure (12) to a second temperature without deforming said second polymeric sheet (14).

9. The method of claim 4 wherein said step of cooling comprises the step of cooling the two-piece structure (12) to remove heat from said two-piece structure without deforming said second polymeric sheet (14).

10. A laminator apparatus for fusing face-to-face sheet materials comprising:
an input nip system (32, 38, 30, 36) through which the materials pass upon entry into the apparatus;
means (68) for heating the sheets while maintaining the sheets in fixed registration wherein the sheets become fully fused together;
an output nip system (20, 34, 30, 36) through which the laminated materials exit the apparatus;
characterized in that the input nip system (32, 38, 30, 36) is adapted to apply pressure to said sheets and to preheat one sheet thereof whereby the sheet materials can be prelaminated prior to lamination in the means for heating the sheets.